1) Field of the Disclosure
The disclosure relates generally to solar layers and solar panels mounted on structures, and more particularly, to assemblies and methods for improved mounting of such solar layers and solar panels on structures.
2) Description of Related Art
Solar technologies are increasingly being used to harvest solar energy and to power various vehicles and devices. For example, solar layers and panels, such as individual photovoltaic solar cells, or solar panel arrays comprised of photovoltaic solar cells, may be mounted to structures, such as transport vehicles and terrestrial and space-based structures, to harvest and convert solar energy into useful outputs such as electrical energy.
Solar powered vehicles are typically vehicles powered completely or significantly by solar energy. Existing solar powered vehicles include solar powered unmanned aerial vehicles (UAVs) that may be capable of achieving flight durations of from several months to years without requiring landing or refueling. Such UAVs typically may employ photovoltaic solar cells located on their exterior surfaces, primarily their wing surfaces, to capture solar energy.
However, the connection or mounting of known photovoltaic solar cells or solar panels to structures, such as solar powered UAVs or other aircraft and vehicles, or terrestrial and space-based structures, may present difficulties.
Known photovoltaic solar cells or solar panel arrays may be brittle and may have limited use if exposed to excessive levels of strain. For purposes of this application, “strain” is defined as a dimensionless measure of deformation of a body and is quantified as a change in length of the body divided by the original length of the body. For example, an object that is one hundred (100) inches long is subjected to one percent (1%) strain if it is stretched one (1) inch. In addition, the strain limit at which known photovoltaic solar cells or solar panels may discontinue working may be well below the strain limit at which a vehicle, such as an aircraft or aerial vehicle, may discontinue working. Thus, the direct connection or mounting of thin photovoltaic solar cells or solar arrays to a vehicle, such as an aircraft or aerial vehicle, may result in the photovoltaic solar cells or solar arrays being forced to approximate the same strain levels as the aircraft or aerial vehicle structure. In turn, this may result in the photovoltaic solar cells or solar arrays ceasing to function properly.
With regard to aircraft or aerial vehicles, strains may be induced on wing mounted photovoltaic solar cells or solar arrays by structural wing flexure resulting from aircraft or aerial vehicle lift loads. Moreover, with regard to aircraft or aerial vehicles, thermal strains may be induced on photovoltaic solar cells or solar arrays if they are bonded or attached to materials with different coefficients of thermal expansion (CTEs) when the temperature changes. For purposes of this application, “coefficient of thermal expansion” means the amount a material will expand for each degree of temperature increase. Different materials expand at different rates, and rates may be expressed as strain per change in temperature. If the connected materials have different CTEs, then the materials may induce thermal strains on each other. If the connected materials have the same or similar CTEs and the materials are subjected to different temperatures, then thermal strains may also be induced in each material.
Further, known thin, planar photovoltaic solar cells or solar panel arrays may be easily deformed to follow a single-curvature shape. For example, such solar cells or solar panel arrays may be curved to follow the wing upper surface airfoil of an aircraft or aerial vehicle. However, unsupported thin solar cells or solar panel arrays may buckle when subjected to compressive strains. Significant buckling may occur even at very low strain levels. Such buckling may disrupt or prevent laminar flow affecting flight characteristics of the aircraft or aerial vehicle or may damage such unsupported solar cells or solar panel arrays. In addition, thin, planar photovoltaic solar cells or solar panel arrays that follow a single-curvature shape may form wrinkles when subjected to compressive strains in a direction perpendicular to the curvature, for example, spanwise compression on a solar cell or solar panel array that follows a wing upper surface curvature. Significant wrinkling may form even at very low strain levels. For purposes of this application, “wrinkling” means a complex buckling pattern with diagonal peaks and valleys, in contrast to a simple buckling pattern with parallel, sinusoidal waves. Such wrinkling may disrupt or prevent laminar flow or may damage such solar cells or solar panel arrays.
In addition, known assemblies and methods exist for connecting or mounting known photovoltaic solar cells or solar panels to surfaces of structures, such as solar powered UAVs or other aircraft and vehicles, or terrestrial and space-based structures. In one known assembly and method for connecting or mounting known photovoltaic solar cells to the surface of a structure, such as a solar powered UAV or aircraft, individual photovoltaic solar cells may be mounted to a wing surface with an adhesive or a double-sided adhesive tape. Gaps between the photovoltaic solar cells may be provided to accommodate strains in the underlying structure without overloading the individual photovoltaic solar cells. The photovoltaic solar cells may be connected electrically with flexible material such as expanded metal mesh. However, with such known assembly and method, the gaps and connections between the photovoltaic solar cells may disrupt laminar flow. Moreover, with such known assembly and method, the cost of mounting or connecting numerous individual photovoltaic solar cells to the wing or other surface of an aircraft or aerial vehicle or other terrestrial and space-based structures, may increase due to increased time, complexity and labor that may be required to mount or connect such solar cells. Finally, with such known assembly and method, forces exerted by the electrical connection between the photovoltaic solar cells on the solar cells themselves may result in the solar cells being thicker and heavier than needed.
In another known assembly and method for connecting or mounting known photovoltaic solar cells to the surface of a structure, such as a solar powered UAV or aircraft, individual photovoltaic solar cells may be cast in a mold with an aircraft wing skin structure, thus becoming a fully integral part of an aircraft wing structure. However, with such known assembly and method, the aircraft wing structure may require reinforcement to limit strain in service to levels below that which may be tolerated by the photovoltaic solar cells. This may result in a substantial increase in the weight of the aircraft wing structure. Moreover, with such known assembly and method, solar cells may be difficult to remove and replace. Thus, a damaged solar cell may result in the entire aircraft wing being scrapped or may result in a costly repair process. Finally, with such known assembly and method, it may not be known until after the aircraft wing is finished whether the solar cells may be working properly. If the solar cells are not working properly after assembly, for example, if the solar cells are damaged during assembly, this may result in a costly repair process.
Accordingly, there is a need in the art for improved assemblies and methods for connecting photovoltaic solar cells and solar panel arrays to structures, for reducing strains on the solar cells and solar panel arrays, and for providing advantages over known assemblies, devices and methods.